The present invention relates to an improved magnetoresistive effect element for reading information magnetically stored in a magnetic recording medium, and an improved shield magnetoresistive effect sensor using the magnetoresistive effect element.
The magnetoresistive effect element is capable of sensing variations of resistance, which may be regarded to be a function of intensity of magnetic flux. The magnetoresistive effect sensor is capable of detecting magnetic signals through the magnetoresistive effect element for reading out of data magnetically stored in a magnetic recording medium at a large linear density. The conventional magnetoresistive effect element utilizes the anisotropic magnetoresistive effect element which is defined to be a phenomenon of variation in resistance of the element proportionally to the square of cosine of an angle defined between a magnetization direction and a sensing current flowing through the element. The anisotropic magnetoresistive effect is described in detail by D. A. Thomson et al. "Memory Storage and Related Applications", IEEE Transaction on Mag. MAG-11, p. 1039 (1975). The magnetoresistive effect sensor using the magnetoresistive effect element is often applied with vertical bias in order to suppress Barkhausen noises. This vertical bias may be applied to anti-ferromagnetics such as FeMn, NiMn, and nickel oxide.
In recent years, a magnetoresistive effect element having a spin valve film has been developed. Such magnetoresistive effect element having a spin valve film utilizes a giant magnetoresistive effect. This giant magnetoresistive effect is a phenomenon of variation in resistance of the element both due to a spin-conservative transmission of conduction electrons between ferromagnetic layers which sandwich a non-magnetic layer and due to a spin-conservative scattering of the conduction electrons on interfaces between the ferromagnetic and non-magnetic layers. This magnetoresistive effect element shows variation in plane resistance between the ferromagnetic layers isolated by the non-magnetic layer in proportion to the cosine of an angle defined between the magnetization directions of the two ferromagnetic layers. As compared to the anisotropic magnetoresistive effect element, has second occurance the giant magnetoresistive effect element improved sensitivity and shows a larger variation in resistance.
In Japanese laid-open patent publication No. 2-61572, it is disclosed that a laminated magnetic structure shows a large. magnetoresistance variation due to anti-parallel order of magnetization in the magnetic layers. Ferromagnetic transition metals and alloys thereof are available for the laminated structure. It is further disclosed that an antiferromagnetic layer is added to one of the paired ferromagnetic layers isolated by the intermediate layer. FeMn is suitable for the anti-ferromagnetic layer.
In Japanese laid-open patent publication No. 4-358310, it is disclosed that the magnetoresistive effect element has two thin ferromagnetic layers isolated by a thin non-magnetic metal layer, where if an applied magnetic field is zero, then the magnetization directions of the two ferromagnetic thin layers are different by the right angle The two ferromagnetic layers isolated from each other by the intermediate layer vary in resistance in proportion to the cosine of an angle defined between the magnetization directions of those two layers but independently from a direction of current flowing through the sensor.
In Japanese laid-open patent publication No. 6-203340, it is disclosed that the magnetoresistive effect sensor has two ferromagnetic thin layers isolated by a non-magnetic metal thin layer, where if an externally applied magnetic field is zero, then anti-ferromagnetic layers adjacent to each other are kept to differ in magnetization direction by the right angle.
In Japanese laid-open patent publication No. 7-262529, it is disclosed that a spin valve comprises laminations of a first magnetic layer, a non-magnetic layer, a second magnetic layer and an anti-ferromagnetic layer. The first and second magnetic layers are made of CoZrNb, CoZrMo, FeSiAl, FeSi, or NiFe which is undoped or doped with Cr, Mn, Ni, Cu, Ag, Al, Ti, Fe, Co or Zn.
If the magnetoresistive effect head or transducer is operated for reproducing at a constant sense current value, then an output thereof is proportional to the amount of variation in resistance of the element. This amount of variation in resistance is defined to be the product of the rate of resistance variation and the resistance of the element. Thus, the output is large as the resistivity of the element is high. In order to increase the output of the magnetoresistive effect head or transducer, it is required to increase the resistance of the element with keeping a rate of resistance variation which is equal to or higher than the rate of resistance variation of the conventional element. In order to achieve this issue, it is effective to use materials having a high resistivity such as amorphous alloys. If, however, the materials having a high resistivity such as amorphous alloys are used for a pinned magnetic layer, then a unidirectional anisotropy of magnetic field applied from an anti-ferromagnetic layer to the pinned magnetic layer is small.
In the above circumstances, it had been required to develop an improved magnetoresistive effect element free from the above problems and disadvantages, namely to obtain a large reproducing output with a sufficiently large exchange-coupling magnetic field from the anti-ferromagnetic layer to the pinned magnetic layer